1. Field of the Invention
The present invention relates to a communication system comprising data terminal devices where the data communication quantity is varied according to time, and more specifically, to a dynamic band variation unit and a switching method of a data communication quantity in a dynamic band variation unit used in the above communication system, allocating the data from the data terminal device to a plurality of lines for communication of the data according to the data communication quantity of the lines.
2. Description of the Prior Art
Heretofore, as a dynamic band variation communication method connecting a dynamic band variation unit coupling a data terminal device to another dynamic band variation unit connected to a data terminal unit through multiple lines, there is known a communication method wherein during communication of data from one data terminal device to an opposing data terminal device through one communication line, another communication line is connected, and the data to be transmitted is allocated to the multiple lines so that the transfer speed of the data is increased. In this case, a clock provided to the data terminal device is increased, and the data to be transmitted is temporarily stored in the dynamic band variation unit, so as to absorb the line delay generated between the plurality of lines. Then, the stored data is transmitted to the opposing data terminal device, thereby realizing dynamic band variation communication utilizing a plurality of lines.
When the number of communication lines being used is decreased by disconnecting a line while communicating data through a plurality of lines in the prior art dynamic band variation communication method, either the data communicated through the disconnected line is cancelled, or the clock provided to the data terminal device from the dynamic band variation unit is reduced according to the band being reduced when disconnecting the line, and the data stored to the device is cancelled.
However, according to the conventional method, there was a problem that the data to be transmitted from the data terminal device was not guaranteed. That is, some of the data transmitted from the data terminal device were lost when reducing the number of lines being connected, or data other than the data transmitted from the data terminal device were inserted in the data from the data terminal device when increasing the number of lines to be connected.
Therefore, according to the conventional method, the data communicated between the data terminal devices may become defective, and only a unit having a retransmission means was able to guarantee such data.